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UV Exposure Risk Estimator

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About This MicroSim

The gap between how a day feels and how much ultraviolet it carries causes real harm, and it is a direct consequence of the spectral physics in this chapter.

Three bars sit side by side and are deliberately allowed to disagree:

  • UV index, on the standard five-band scale, with a time-to-sunburn readout.
  • Perceived brightness, from the visible irradiance reaching you.
  • Perceived warmth, from the air temperature.

Two presets make the point on their own:

  • Ski slope, March, noon - 2500 m, fresh snow, clear sky. UV index 7.2 at minus 6 °C. Unprotected skin burns in about half an hour, on a day you need a coat for. The index is calculated for a flat surface; upward-facing skin gets roughly 80 per cent again on top of it from snow reflection, which is why skiers burn under the chin.
  • Overcast summer noon - UV index 3.7 with brightness at 1.7 out of 10. Cloud takes 85 per cent off the visible light and only 65 per cent off the UV. It looks like a day you cannot burn on. It is not.

Where the number came from breaks the result into its parts: the clear-sky value for the current solar angle, then altitude, cloud, ground reflection and ozone as separate percentages. Altitude adds about 6 per cent per 1000 m. Fresh snow adds 20 per cent to the horizontal index. A low-ozone episode adds 31 per cent.

Build your own from the chips - latitude, date, cloud, ground and ozone - and use the time and altitude sliders. Then look at the three bars and ask which one you would have guessed from.

How to Use

  • Press a preset and read the verdict, then look at all three bars together.
  • Build a scenario with the chips on the left, and drag the time and altitude sliders.
  • Change only the cloud setting and watch the brightness bar collapse while the UV bar barely moves. That is the mechanism.
  • Set the ozone to Low and see what a depleted column does.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

<iframe src="https://iowerx.github.io/pi-env-monitor/sims/uv-exposure-estimator/main.html"
        height="672px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

6-12

Duration

20-25 minutes

Bloom's Taxonomy Level

Evaluate (L5)

Prerequisites

  • Chapter 9 sections on the solar spectrum
  • The Solar Energy Budget MicroSim

Activities

  1. Break the warmth rule (6 min): Find two scenarios with the same UV index and very different temperatures. Write down what makes them differ.
  2. Break the brightness rule (7 min): Starting from a clear summer noon, change only the cloud. Record UV and brightness for all three settings. Which falls faster, and by how much?
  3. Assess a real plan (8 min): You are going walking at 2000 m in June at 45 degrees north, with patchy cloud, on a snowfield. Build it, read the time to burn, and write a two-sentence recommendation.

Assessment

  • Assesses UV risk from time, place, altitude and surface rather than from appearance.
  • Explains why cloud is a poor guide to UV.
  • Identifies snow and altitude as risk multipliers.

References

  1. WHO, Global Solar UV Index: A Practical Guide (2002) - the definition of the index and the five risk bands.
  2. US EPA: UV Index - the band colours used on the gauge.
  3. Wikipedia: Ultraviolet index
  4. WMO: ozone and ultraviolet radiation - why a low-ozone episode raises ground UVB.